1. Field of the Invention
The present invention relates to titanium-silicalite molecular sieves and methods for preparing the same, and more particular to, a titanium-silicalite molecular sieve having a metal selected from IIA to IVA elements and a method for preparing the same.
2. Description of the Prior Art
Crystalline titanium-silicalite molecular sieves are formed by incorporating titanium into the zeolite structure of silicon dioxide. TS-1 molecular sieves have the MFI structures, and TS-2 molecular sieves have the MEL structures. These molecular sieves are used in oxidation reactions such as ammoximation of cyclohexanone and hydroxylation of phenol which use hydrogen peroxide as the oxidant.
Cyclohexanone oxime is the intermediate of the preparation of amides. U.S. Pat. Nos. 4,968,842, 522,752, 5,312,987 and 6,828,459 disclose using cyclohexanone, ammonia and hydrogen peroxide to form cyclohexanone oxime. However, in such methods, the usage efficiency of hydrogen peroxide is about 89% to 90%. The usage efficiency of hydrogen peroxide cannot be improved for lowering the production cost.
EP226257, EP266825 and EP226258 disclose methods for preparing a titanium-silicalite molecular sieve having a metal. EP226258 discloses that the iron source is treated with ammonia to form a hydroxide precipitation, the hydroxide precipitation is washed by water, neutralized, filtered, dissolved in the template agent, mixed with the titanium-silicon solution, and then heated to form the molecular sieve. Such method is complicated. EP266825 discloses that the gallium source is dissolved in ethanol, then mixed with the titanium-silicon mixture and template agent solution, and heated to form the molecular sieve. However, the gallium mixed with the titanium source and the silicon source would result in the white turbid product. The white turbid product is dissolved in the template agent. The template agent is in an aqueous form, but the dissolution of titanium is different from the dissolution of silicon. Thus, the order of the molecular sieve is decreased and the catalyst property is thus destroyed. EP226257 discloses that the aluminum source is dissolved in the template agent, then mixed with the titanium-silicon solution, and heated to form the molecular sieve. Similarly, the aluminum source mixed with the titanium source and the silicon source would result in the white turbid product. The white turbid product is dissolved in the template agent. The template agent is in an aqueous form, but the dissolution of titanium is different from the dissolution of silicon. Thus, the order of the molecular sieve is decreased and the catalyst property is destroyed.